Abstract Detail

Several long-term datasets have shown that first flowering dates of many temperate plant species are advancing in association with recent climate change, with more rapid advancements in spring compared to summer. However, it is unclear whether other aspects of flowering phenology,such as peak flowering and duration of flowering (last minus first date of flowering), mirror changes in flowering onset. Understanding how entire phenological phases are changing, as opposed to distributional extremes like first flowering, will allow for more accurate predictions of ecological responses to climatechange. We use a 36-year record of flowering phenology collected at the Rocky Mountain Biological Laboratory (2900m a.s.l.) to describe how multiple aspects of flowering phenology are changing through time in a subalpine plant community. Recent studies have shown that snowmelt is occurring earlier and temperatures are increasing at our study site. The number of flowers on all plant species present was counted in permanent 2 x 2m plots every other day throughout the growing season, spanning the years 1974-2011. We examined 71 of the 120 plant species present in our long-term record (species present in at least half of our sample years). First and peak flowering are generally advancing (44% and 27% of species show significant shifts, respectively), but duration of flowering is changing in unpredictable ways. Only for first flowering are phenological shifts more pronounced in spring vs. summer, while changes in peak flowering, last flowering, and duration do not differ between spring and summer. Shifts in spring flowering, however, are consistently less variable. Various changes in last flowering dates relative to flowering onset are causing changes and shifts in the flowering duration of individual species (significant changes in 35% species): changes only in duration (flowering extended in 13 species, shortened in 2 species), advancement of entire flowering period (6 species), and simultaneous changes and shifts (flowering extended plus entire flowering period advanced in 3 species, flowering shortened plus entire flowering period advanced in 1 species). First and peak flowering associated more strongly with snowmelt than temperature, whereas last day of flowering associated more strongly with temperature, which may account for some of the interspecific variation in changes in flowering period. Our results present a more complicated picture than conclusions drawn from studies of flowering onset. These idiosyncratic changes in phenology could have major implications for ecological interactions among plant species and between plants and their mutualists and herbivores.